1. Field of the Invention
The invention relates to flame-retardant molding compositions and molded articles made from thermoplastic polyamides.
2. Description of the Related Art
The prior art recommends halogen compounds, usually in combination with antimony trioxide or formulations containing antimony trioxide, as flame retardants for the production of flame-resistant polycondensation products, e.g., see U.S. Pat. No. 3,418,267, German Published Patent Application No. 16 94 494, German Published Patent Application No. 19 31 387 (which corresponds to U.S. Pat. No. 3,778,407), and German Published Patent Application No. 25 44 219 (which corresponds to U.S. Pat. No. 4,076,682), the disclosures of which are incorporated herein by reference.
In spite of the fact that halogen compounds are very effective as flame retardants, their use entails considerable disadvantages. These are described in detail in European Patent No. 00 44 419 (which corresponds to U.S. Pat. No. 4,396,736) and the German Patent No. 32 08 486 (which corresponds to British Patent No. 2,097,008), the disclosures of which are incorporated herein by reference. If perbrominated aromatic compounds, such as, e. g., decabromodiphenyloxide, are used, a particularly serious disadvantage is the generation of toxic compounds such a dioxins and furanes during combustion which presents a severe public health hazard.
Apart from halogen compounds, the use of elemental phosphorus is known for imparting flame-resistant properties to thermoplastic materials, mainly to polyamide. This method is described in German Published Patent Application No. 11 73 641 and in U.S. Pat. No. 3,951,908, the disclosures of which are incorporated herein by reference. Here, a number of drawbacks must also be accepted during combustion, such as the generation of phosphine. Furthermore, color, as well as electric properties, of the polymeric materials employing such flame-retardants are influenced negatively. European Patent No. 00 44 419-B mentioned above provides information regarding this point.
Magnesium hydroxide and aluminum hydroxide, as well as nitrogen-containing compounds, such as melamine, melamine cyanurate and cyanoguanidine, are only suitable as flame retardants for polyamides under certain conditions. They must be used in large volumes in order to attain a satisfactory V0 rating according to Underwriter Laboratories specification UL-94. This changes the mechanical properties of the polyamides considerably, however.
Such flame retardants are proposed, inter alia, in U.S. Pat. No. 4,263,203, U.S. Pat. No. 4,001,177, German Published Patent Application No. 29 37 379 (which corresponds to U.S. Pat. No. 4,001,177), German Published Patent Application No. 16 94 254 (which corresponds to U.S. Pat. Nos. 3,084,135 and 3,270,016), German Patent No. 41 27 112, and German Published Patent Application No. 39 09 145, the disclosures of which are incorporated herein by reference.
U.S. Pat. No. 3,789,091 and U.S. Pat. No. 3,849,368 describe ring-shaped phosphoric acid esters as flame-retarding additives for various homopolymers, as well as for PA 6,6. The teachings of these patents do not lead to the solution of the special problems of providing polyamides which meet V0 standards. In semicrystalline polyamides, such compounds have the disadvantage of exhibiting a distinct migration.
It is therefore the object of the present invention to provide a polyamide, i.e., a polyamide composition, which is flame-retardant and meets V0 standards.
It is a further object of the present invention to provide flame-retarding molding materials and/or molded articles made from such a polyamide, which have good mechanical and thermal properties that meet the V0 standards according to UL-94.
It is yet another object of the present invention to provide flame-retarding molding materials and/or molded articles made from such a polyamide that do not exhibit any or substantial any migration of flame-retarding additive and, compared to polyamide containing no flame-retarding additive, have electrical properties which remain substantially unchanged.